1. Field of the Invention
This invention relates in general to an information recording device for an optical disc medium, for example, a reproduction-only DVD (digital video disc, or disc versatile disc) medium such as a DVD-Video or a DVD-ROM, or a DVD-Recordable (DVD-R) with format exchangeability.
2. Description of Related Art
As multimedia gets more popular than ever, reproduction-only medium such as DVD-Video or DVD-ROM, or information recording medium such as write-once-type DVD-R using coloring matter as a recording layer is developed.
Information (sector, for example) recorded on such DVD medium is a format as shown in FIG. 9A. As shown in FIG. 9D, in this format, data is continuously recorded with a constant linear density on the whole track of the medium. Conventionally, the controlling method for the rotational velocity of the information recording medium uses a CLV (constant linear velocity) manner as shown in FIG. 9B to make the reproduction-only medium or the information recording medium with the exchangeability format. The rotational velocity of the medium is controlled in a manner that the rotational number is inversely proportional to the track radius. Information is recorded with a constant frequency of a recording channel clock, while the linear velocity of the track is constant.
When the recording is performed in the CLV manner, the recording can be done with different speeds by varying a predetermined recording linear velocity with a fixed magnifying power. In general, the standardized optical recording medium is specified by a predetermined recording linear velocity. For DVD-R, one-fold speed corresponds to a recording linear velocity of 3.49 m/sec and the recording clock frequency is 26.16 MHz. In an information recording device using such an optical recording medium, new recording conditions are set inside the information recording device for setting a higher recording speed, but it is necessary to use an independent recording manner to record information such that the reproducing signals have a low jitter characteristic.
However, in general, for the DVD-R medium of coloring matter system where the marks (pits) are formed according to the heating mode, because the pulse width and the recording power of the recording pulse caused by light-emission during the recording for each particular recording linear velocity are different in the optimum values, the status of the formed marks or spaces are changed for different recording linear velocity.
Namely, a condition where an insufficient amount of heat for the leading heating portion to form the mark occurs, and the heating temperature to reach an optimum decomposition temperature is different, so that the average length of the mark is spread in a wide range. Therefore, the ratio to the recording clock period T of the optimum heating pulse is different and therefore a uniform mark width cannot be obtained. As a result a thin or thick mark (i.e., tear-shaped mark) is created, so that the jitter characteristic degrades.
In this regard and according to Japanese Laid open Publication No. 2001-155339, when the recording onto an optical disc of coloring matter system (such as a DVD-R) is performed, a rectangular pulse is essentially used. At this time, the recording power and the light-emission pulse width are changed according to the recording linear velocity.
In addition, according to Japanese Laid Open No. 2001-176073, when the optical disc of coloring matter system such as DVD-R is recorded, a rectangular pulse is used. At this time, two kinds of recording power levels and the light-emission pulse width only when the mark length is shortest are changed according to the recording linear velocity.
This recording method is effective in lowering recording lower for the optical disc of coloring matter system. However, for the recommended recording linear velocity, the multi-pulse recording is determined according to the specification. It does not consider the recording waveform with respect to the variation of the optimum recording power that is caused by the wavelength shift of the light source due to the recordable speed or the temperature variation in the device of the information recording device.
Namely, the above cases provide a control in a manner that setting values of elements of a recording pulse train, such as the light-emission pulse's duty ratio etc., are variable according to the recording linear velocity. However, there is a limitation in the settings of the pulse widths and the allowable values of the recording powers that the information recording device sets. Even though the settings are based on the recording condition assigned by pre-formatted information of the optical disc medium, there is difficulty in setting the optimum recording condition.
Namely, when the recording sensitivity of DVD-R, etc. using coloring matter is reduced because the wavelength of the output laser beam shifts to the long wavelength side, the optimum recording power obtained by the test writing, etc. is deviated by the wavelength shift, so that a good recording is difficult to obtain. In addition, even though a correction function for the recording power according to the mark forming status during the recording, a so-called Running-OPC (Running-optimum power calibration), is used, the sensitivity reduction due to the wavelength shift is created about 3% per 1 nm.